A conventional light source such as, for example, an incandescent lamp or halogen lamp, when dimmed, acts like a near exact black body radiator and follows the Planckian curve on the 1931 CIE Chromaticity Diagram. For example, a conventional incandescent lamp at its maximum output may output light having a color temperature of 3000K. As that incandescent lamp is dimmed (e.g., through use of a triac dimmer), the current running through its filament is reduced, resulting in a lower, warmer color temperature (e.g., 2000K).
As solid state light sources become more widely used, lighting designers and lighting consumers desire that the solid state light sources behave similarly to conventional light sources. However, unlike an incandescent lamp or a halogen lamp, solid state light sources typically hold their color temperature as they are dimmed. This behavior has been overcome to a degree by using a color mixing technique. A two channel controllable current solid state light source driver performs color mixing between two strings of solid state light sources to achieve incandescent-like dimming (i.e., dimming at or substantially near the Planckian curve), as desired by the market. An example of such a lamp is the Philips® Master LEDspotMV GU10 Dim Tone lamp, which was designed to operate at 220V/230V systems with a triac dimmer.